(1) Field of the Invention
The present invention pertains to a method and a device for regenerating the integrity of the bit rate in a plesiosynchronous (i.e. nearly synchronous) system.
(2) State of the Prior Art
A data communication network or a pulse code modulation (PCM) telephonic network is said to be plesiosynchronous when the switching centers located along the path of a link between two subscribers have bit rates which are unequal yet very close to each another. The result of this is that each center sends its immediate neighbour a little more or a little less data than the latter is capable of handling. The reception will be said to be hyposynchronous when the clock frequency of the receiver is slightly lower than that of the transmitter, and the receiver will therefore necessarily lose data. In the opposite situation, the reception will be called hypersynchronous. In this case, the receiving sector will not receive sufficient data, and it will have to fill in the gaps with filler bits which are generally "unintelligible".
The receiving circuit of a subscriber receives, in a given time interval, a number of bits which is different from the number transmitted by its correspondent.
It will be said then that the network does not comply with the integrity of the bit rate of the message. This does not affect normal PCM phonic links where certain samples of speech may be skipped or repeated without altering the intelligibility of the message between the disturbances. However, for links which are scrambled from end to end, the loss of bit rate integrity means that the encoded message is shifted away from the decoding key, causing a total loss of intelligibility.